Going back to crop sensor from FF

I have briefly returned to shooting with a crop sensor camera to get that additional reach. This was shot using a 70-200mm lens + a 2x converter (resulting in a 600mm reach).
I had forgotten how forgiving it is to shoot with the Nikon D300 compared to the D800, my D300 is worn and torn and I am now seriously contemplating buying the Nikon D500 to have as a complement to my Full frame. The benefits beside the reach would be the speed and supposedly superior autofocus system.